The present invention relates to the art of electrical switching devices and more particularly to an hydraulic relay using mercury in a hermetically sealed chamber to establish electrical continuity between two conductors.
The invention is particularly applicable for use in high power electrical relays and it will be described with particular reference thereto; however, it is appreciated that the invention has much broader applications and may be used in various switching devices for establishing electrical current between two spaced conducting elements. In many relays which carry a substantial amount of current there are provided movable metallic contacts that engage fixed contacts. When the contacts are opened, there is a tendency to arc. This can erode the contacts. In addition, after long use the contacts often become dirty and contaminated which prevents tight engagement and also changes the electrical characteristics. In an attempt to overcome the difficulties of using the metal contacts, some relays employ a mercury pool or use mercury wetting of the contact area to reduce the arcing during operation of the contacts. The use of mercury does reduce the tendency of arcing and does maintain a certain amount of uniformity of electrical resistance and other characteristics during prolonged use of the relay; however, the use of a mercury pool has presented certain undesirable features. For instance, the relay may be sensitive to orientation or position. Thus, the relay must be mounted in a certain position. Also, mercury in relay structure is susceptible to vibrations and shock which will distract from its universal usefulness. Generally, the relays having a mercury pool at the metal contacts use the metal contacts themselves for the conductive path. Initially, this use of mercury to prevent erosion is quite successful; however during prolonged use there must be provisions for replenishing the film used in the contact area. A sample of this type of unit is illustrated in Pollard U.S. Pat. No. 2,454,406.
Mercury also has been used in electrical switches by employing a body of mercury itself as the actual interconnecting conductor between two fixed contacts. Such a system is shown in Young U.S. Pat. No. 2,766,396. In this instance, a wire gauze is incorporated to prevent damage to the fragile enclosure by the mercury during shipment and other times of extreme vibration. Still a further prior patent showing the use of a mercury pool as the actual interconnecting conductor between adjacent fixed conductors is Hancock U.S. Pat. No. 2,695,938 and O'Neil U.S. Pat. No. 2,721,317. In each of these instances, a bellows is used to force mercury into a conducting position. Release of pressure from the bellows allows the mercury to break electrical contact through the mercury bath and disconnect the electrical conductive path. It is with this background regarding the use of mercury in an electrical switching device that the present invention has been made.